The present invention relates to cosmetic compositions comprising select conjugated dienes, which, when topically applied to animal, including human, skin provide protection from the chronic effects of prolonged exposure to sunlight.
A variety of physiological responses to ultraviolet radiation have been observed, and various methods of controlling the harmful responses have been provided. The most well recognized responses include, for example, immediate responses such as the generation of erythema (sunburn) followed by reversible pigmentation or melanization, and chronic responses such as wrinkling, creasing, and carcinoma of the skin. In general, it is believed that both immediate and chronic responses occur as a consequence of varying degrees of exposure to ultraviolet radiation in the range of 2950A to 4000A. Within this range, ultraviolet radiation is able to penetrate the outer protective layers of the skin.
One means of controlling undesirable responses to ultraviolet radiation is to avoid exposure to sunlight for more than short periods of time. However, most people enjoy outdoor recreation and admire melanization of the skin. Moreover, some degree of insolation is desirable to insure adequate Vitamin D synthesis. Accordingly, previous research has focused on methods of controlling the more immediate erythemogenic responses, thus enabling people to enjoy exposure without undue discomfort or irritation. Commercially available "suntanning" preparations mitigate the dosage of erythemogenic radiation which penetrates the outer skin thereby allowing the tanning response while preventing severe erythema. A wide variety of ultraviolet reflecting and absorbing agents are known and disclosed in the prior art.
Although suntanning preparations enable people to enjoy outdoor activities without discomfort, such preparations also mute the natural warning system which calls attention to the prospect of chronic damage. As a consequence of the prolonged periods of exposure, encouraged by reduced erythemogenic response, absorbed ultraviolet radiation is believed to cause chronic changes in the epidermis. Hyperkertinization, which constitutes the major natural defense to prolonged exposure; increased marking of the skin; areas of pigmentation and atrophy; superficial scaling and telangiectasis or tumorous swelling of the small blood vessels constitute some of the visible signs of chronic damage. The development of skin cancer or pre-cancerous lesions (actinic keratoses) is also known to be induced by extensive exposure to erythemogenic radiation.
Accordingly, while known compositions comprising sunscreening and ultraviolet radiation absorbing agents provide relief from the more immediate erythemogenic response, the chronic effects of prolonged exposure to sunlight remain substantially unaffected.